<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>响应式布局</title>
    <style type="text/css">
        @media only screen and (max-width: 374px) {

            /* iphone5 或者更小的尺寸，以 iphone5 的宽度（320px）比例设置 font-size */
            html {
                font-size: 86px;
            }
        }

        @media only screen and (min-width: 375px) and (max-width: 413px) {

            /* iphone6/7/8 和 iphone x */
            html {
                font-size: 100px;
            }
        }

        @media only screen and (min-width: 414px) {

            /* iphone6p 或者更大的尺寸，以 iphone6p 的宽度（414px）比例设置 font-size */
            html {
                font-size: 110px;
            }
        }

        body {
            font-size: 0.16rem;
        }

        #div1 {
            width: 1rem;
            background-color: #ccc;
        }
    </style>
</head>

<body>
    <div id="div1">
        this is div
    </div>
</body>

</html>